Ramp Loading; Capacity Override; Compressor Minimum Speed Override; Vaporizer Temperature Control - Carrier AquaEdge 23XRV Start-Up, Operation And Maintenance Instructions Manual

more detail on the alarm condition. Since there may be more
than one alarm condition, another alarm message may appear
after the first condition is cleared. Check the ALARM HISTO-
RY screen for additional help in determining the reasons for the
alarms. Once all existing alarms are cleared (by pressing the
softkey), the default ICVC display returns to normal
RESET
operation.
The ramp loading feature controls the
Ramp Loading —
rate at which the compressor loads up. This control can prevent
the compressor from loading up too fast during the short period
of time when the chiller is started and the chilled liquid loop
has to be brought down to the CONTROL POINT. This helps
reduce electrical demand charges by slowly bringing the
chilled liquid to the CONTROL POINT.
The PIC III control system provides two methods of ramp
loading. Ramp loading can be based on chilled liquid tempera-
ture or on motor load. The method of ramp loading is selected
from the RAMP__DEM screen.
1. Temperature ramp loading (TEMP PULLDOWN DEG/
MIN) limits the degrees per minute rate at which either
the leaving chilled liquid or the entering chilled liquid
temperature decreases. This rate is configured by the
operator on the TEMP_CTL screen. The lowest tem-
perature ramp rate will be used if chiller power has
been off for 3 hours or more (even if the motor kilo-
watts ramp loading is selected as the ramp loading
method).
2. Motor load ramp loading (AMPS OR KW RAMP %/
MIN) limits the percent per minute rate at which the
compressor motor current or compressor motor load
increases. The AMPS OR KW RAMP %/MIN rate is
configured by the operator on the RAMP_DEM screen
in amps or kilowatts.
If kilowatts is selected for the DEMAND LIMIT SOURCE,
the MOTOR RATED LOAD KILOWATTS must be entered
(information found on the machine Electrical Data Nameplate)
in the VFD_CONF screen.
The TEMP PULLDOWN DEG/MIN may be viewed or
modified on the TEMP_CTL screen which is accessed from the
EQUIPMENT SERVICE screen. PULLDOWN RAMP TYPE,
DEMAND LIMIT SOURCE, and MOTOR KW RAMP %/MIN
may be viewed or modified on the RAMP_DEM screen.
Capacity Override (Table 6) —
overrides are available to prevent the chiller from exceeding
some limits and going into an alarm state. Alert messages 120
through 127 are displayed on the ICVC when capacity
overrides are in effect. Capacity overrides can prevent some
safety shutdowns caused by exceeding the refrigerant low
temperature safety limit, motor high temperature safety limit,
Adjustable capacity
48
and condenser high pressure limit, high VFD inverter rectifier
temperature limit, and high VFD inverter temperature limit.
Compressor Minimum Speed Override —
This capacity override increases compressor speed if oil vis-
cosity falls below acceptable levels or if conditions exist that
will prevent sufficient refrigerant cooling to the VFD or mo-
tor. This override is not configurable, it is the only override that
will increase chiller capacity to avoid a safety shutdown.
Compressor minimum speed override is most likely to happen
at evaporator temperatures of 50 degrees or more, combined
with low speed, low lift, and less than 25% tons.
The PIC III controls regulate the minimum allowable com-
pressor speed based on oil sump temperature and pressure and
on compressor head. The compressor bearings require higher
oil viscosity when operating at low speed than they do when
operating at high speeds. The controls increase compressor
speed when the oil viscosity is too low to operate the compres-
sor at the lower speed. The low compressor speed override is
also enabled at low loads with high condensing pressure.
Vaporizer Temperature Control COMPRES-
The vaporizer temperature control is regulated
SOR ON —
by the PIC III using the vaporizer heater relay and a flexible
surface heater that is attached to the bottom of the vaporizer.
The vaporizer heater relay is energized whenever the compres-
sor is at low speed and requires additional heat to maintain a
sufficient vaporizer temperature. The vaporizer heater is turned
off when the additional heat is no longer required. The vaporiz-
er heater is not energized when the chiller is not running. The
vaporizer heater also uses the values configured in the SET-
UP3 table for TURN ON SPEED and TURN ON LIFT, TURN
OFF SPEED and TURN OFF LIFT to allow the service techni-
cian to adjust the heater control based on either compressor
speed or the lift across the cooler and condenser.
Oil Sump Temperature Control COMPRES-
The OIL SUMP TEMP is regulated by the
SOR OFF —
PIC III control module using the (1C) oil heater relay and an
immersion heater in the oil sump. The oil heater relay is ener-
gized whenever the chiller compressor is off, and the OIL
SUMP TEMP is less than 140 F (60 C) or whenever the OIL
SUMP TEMP is less than the CALC EVAP SAT TEMP plus
53 F (29.4 C). The oil heater is then turned off when the OIL
SUMP TEMP is:
1. More than 152 F (66.7 C) or
2. The OIL SUMP TEMP is more than 142 F (61.1 C) and
also warmer than the CALC EVAP SAT TEMP plus
55 F (30.6 C).